Aerial lifts are commonly used in the electric utility industry to facilitate work at an elevated position in several areas such as utility pole, telephone or power lines, street lights, building walls, etc. Such aerial lifts typically boast work platforms (e.g., a workstation in the form of a bucket) coupled to wheeled vehicles through a multiple section-boom that is adapted to elevate and orient the aerial platform which carries the personnel who can perform the requisite work. The personnel also typically control the operation of the lift from the aerial platform or bucket through a control assembly that is coupled to the bucket and that includes several handles which can be used to manipulate the position and orientation of the bucket by controlling, among others, the multi-section boom. The control assembly may be equipped with other handles that can be used to control material handling equipment or other tools that may be removably attached to bucket (e.g., a jib, winch, drill, saw). The American National Standards Institute (ANSI) Accredited Standard Committee has issued standards pertaining to such aerial lifts which are known as ANSI A92.2.
Commonly, aerial lifts utilize hydraulics systems to control bucket movement and equipment. As such, the control assembly typically includes control valves connected to handles, as well as hydraulic fluid that flows through these valves and through fluid conduits which mostly extend along the boom section in order to translate control inputs from the handles into corresponding component movement that enables the bucket and equipment to operate as desired. Much like many components in the control assembly, the valves to which the control handles are connected are typically constructed of an electrically conductive material. Moreover, these components are located in close proximity to, if not in physically contact with, the boom section which incorporates structural material (i.e., typically an electrically conductive metal such as steel and/or aluminum) so as to have sufficient structural strength to support the bucket and personnel. The boom section typically rests on a vehicle which, needless to say, is also made of several metal parts in physical contact with the ground. Thus, the control assembly, including many of its components, may be considered electrically connected to the ground.
Because the bucket may be positioned close to highly-charged electrical lines, all of the aforementioned control handles disposed within the bucket's vicinity (which are often referred to as upper controls) ought to be as electrically isolated as possible in order to prevent electrocution of any personnel or operator(s) that may come in contact with the electrical lines and the handles or otherwise fail to comply with safety measures and regulations. To this end, ANSI Standard A92.2 standards state that such upper controls should be equipped with high electrical resistance components. Existing techniques to provide high electrical resistance include using materials that are substantially non-conductive, such as plastic or similar composites, to construct the handles and portions with which personnel may come in contact. However, such materials (even when reinforced) tend to not have sufficient structural strength and rigidity to withstand continuous manipulation by operators who apply enough force on the handles, causing the handle bodies to twist in undesirable directions, or even break. On the other hand, cost-effective materials having sufficient rigidity and durability typically include metal or some form of conductive substance, and therefore risk causing electrocution to the personnel by creating a discharge path from the handle to the ground, if the handle is not substantially isolated from other contiguous portions that are electrically connected to the ground, as described above. Therefore, it is desirable to provide high electrical resistance for control handles such that they are substantially electrically isolated from other contiguous portions in the control assembly, conduits or boom section, while maintaining the ability to construct the handles from electrically conductive material so as to preserve structural rigidity of the handles.
Moreover, it is common and often advantageous for other portions in the control assembly to be constructed from electrically conductive material. For example, the valves and/or portions of fluid lines can be made of metal so that they may have sufficient thermal and structural properties to withstand hydraulic fluid movement at varying conditions. However, these other components of the control assembly also pose a risk of electrocution given that they can be electrically connected to the handles and the ground, as specified above. Furthermore, these components pose another risk since they may come in contact with a tool handled by the personnel and therefore create a discharge path from the tool grip to grounded control assembly components (e.g., the blade of a saw improperly placed through an opening in the control panel may extended downwards into the inner portions of the assembly and come in contact with one or more fluid lines.) Therefore, it is further desirable to provide a mechanism for providing high electrical resistance for the valves and fluid lines inside the control assembly such that they are substantially electrically isolated from other contiguous aerial lift components such as fluid conduits and/or tools or boom sections along which the conduits extend, while maintaining the ability to construct the valves and fluid lines from electrically conductive material so as to preserve thermal and structural properties.
Therefore, there is a need for mechanisms that provide high electrical resistance for several components of aerial work platforms (particularly ones used in hydraulic lifts), including the upper control assembly and handles in a comprehensive, one-size fits all, and cost-efficient manner that preserves the ability to construct desired components from electrically conductive material.